More than 40,000 containers were transported between the two countries in 2016, up from 35,000 a year earlier and "the largest volume of goods" moved on the iron link so far, Deutsche Bahn (DB) said in a statement.
"This is a good basis from which to increase the number of containers to about 100,000 by 2020," DB board member Ronald Pofalla said.
The trans-Eurasian rail stretch spans a distance of 10,000 to 12,000 kilometres (6,000-7,000 miles), passing through Poland, Belarus, Russia, Kazakhstan and Mongolia before stopping at several Chinese cities.
The journey takes 12 to 16 days, around half the time it would take for the goods to arrive by sea.
Air travel would be fastest but considerably more expensive.
The freight train service has proved especially popular with clients who require urgent but cost-efficient deliveries such as manufacturers of clothing, electronics and car parts, according to DB.
The Germany-China rail line began operating in 2008. Deutsche Bahn now has some 5,000 employees working in China through its freight subsidiary DB Schenker.